The long-range objective of this program is the study of leukocyte function in health and disease. The immediate objective is to further define the molecular and biological properties of potently bactericidal cationic proteins, recently isolated by us from rabbit and human polymorphonuclear leukocytes (PMN). These proteins cause discrete and reversible alterations in permeability and phospholipids of the envelope of susceptible bacteria. The specific aims are: 1) to purify these proteins to homogeneity and to isolate and characterize the subunits of the bactericidal complex rabbit PMN. To this end we will use chromatographic, electrophoretic and immunologic methods. 2) To study binding of radioactively labeled, biologically active proteins to the microbial envelope. 3) To examine envelope properties that determine bacterial sensitivit or resistance to the purified protein. 4) To explore the biological role of bacterial phospholipid breakdown in digestion of bacteria killed by granulocytes. 5) To attempt to delineate specific events involving bacterial structure and function that may underlie the bactericidal action of these PMN proteins.